A New Microwave Mixer Suitable for Use with Very High Intermediate Frequencies (Correspondence)

In the conventional microwave mixer it is generally necessary to provide a low-pass filter or some similar network in the intermediate-frequency output circuit. This filter usually takes the form of a capacitance or choke, which is arranged to present, as nearly as possible, a short circuit to the signal and local oscillator frequencies. For a microwave mixer with an IF of less than 100 Mc chokes have been found to be satisfactory provided that a correct choice of the short-circuit position has been made. It is difficult, however, to design a choke system with a capacitance of less than 5 pf and, even at intermediate frequencies as high as 100 Mc, a capacitance of this value could seriously limit the fractional IF bandwidth or the noise performance attainable. At intermediate frequencies greater than 1000 Mc it was expected that the problems of design of a low-pass filter would be even greater because of the dificuity of meeting the conflicting requirements of efficient RF rejection and lF coupling.